The present invention relates to a coating apparatus, and particularly to an apparatus for applying various types of coating compositions onto a continuously running elongated belt-like support (hereinafter referred to as a "web") used in manufacturing recording materials such as information recording paper, printing paper such as pressure-sensitive paper, heat-sensitive paper, diazo copying paper, and the like; photographic film, photographic light-sensitive materials such as photographic film, photographic paper, and the like; photosensitive printing plates; and magnetic recording materials such as magnetic recording tape and the like. More specifically, the present invention relates to a coating width setting device for a backup device for use when coating is carried out by causing a thin-film-like coating composition to strike against a running web.
A curtain coating apparatus has been known for performing coating by causing a thin-film-like coating composition to strike against a running web. A curtain coating apparatus is arranged such that a free falling curtain film of coating compositions of one or more types strikes against a material to be coated so as to produce a coating film on the material. Curtain coating apparatuses have been used conventionally for applications such as coating furniture and metal plates, but have more recently been applied to high-accuracy, high-speed coating as manufacturing techniques have improved.
As disclosed in U.S. Pat. Nos. 3,632,374, 3508,947, and 4,230,743 and Japanese Patent Unexamined Publications Nos. Sho. 52-74761, and Sho. 52-74762, the curtain coating method has been applied to applications in which high accuracy is required, such as in manufacturing photographic light-sensitive materials, pressure-sensitive copying recording paper, heat-sensitive recording paper, etc., with satisfactory results.
Such a coating apparatus, as shown in FIG. 4, is disclosed in commonly assigned Japanese Utility Model Unexamined Publication No. Sho. 59-176676.
As illustrated in that figure, a thin-film-like flowing layer 5 of a coating composition of at least one type flows along a downwardly slanting slide slope surface 4 and is made to strike against a running web 11 so as to perform coating on the running web 11. A support guiding mechanism, constituted by a rail 12, slide bodies 13, and a driving mechanism 14, is provided with which edge guides 8a and 8b supporting opposite ends of a free falling thin-film-like coating-composition film 6 are moved while maintaining a predetermined gap between a top end lip 7 of the slide slope surface 4 and the edge guides 8a and 8b.
Further, a method of changing a coating width so as to conform with the width of the web being coated is disclosed in commonly assigned Japanese Patent Unexamined Publications Nos. Sho. 60-75354, Sho. 61-477, and Sho. 61-35880.
In such conventional apparatuses, it is required that the entire width of the flowing layer 5 flowing down along the slide slope surface 4 from a slot 3 of a coating composition feeder 1 be made larger than that of the support 11. The free falling curtain film 6 is applied to form a coating with the distance between the edge guides 8a and 8b being set to conform with the width of the support. Surplus coating composition not striking the support is collected.
In the curtain coating method, the free falling curtain film is held at its opposite edges by the two edge guides 8a and 8b. However, if the entire curtain is applied to the support by the use of the edge guides, formation of considerably thicker coating portions occurs at the edge portions of the web than in other portions thereof.
Accordingly, various problems occur in practical use. That is, when the entire curtain is applied on the support, the thicker coating portions produced at the opposite edge portions of the coating layer require a longer drying time than portions of normal thickness. Consequently, if the drying process has insufficient capacity to dry the thicker coating portions, the thicker coating portions are left in a tacky state, causing problems such as the undried coating composition being transferred to the conveying rollers disposed after the drying stage to thereby foul the web in following stages, or the opposite edge portions being bonded when winding the support around a roll in a take-up step, sometimes causing the support may to break when it is unwound in a subsequent cutting step.
To eliminate the problems caused by the formation of thicker coating portions at the opposite edge portions of the coating layer and by the curtain coating having a width greater than that of the support in the conventional curtain coating, commonly assigned Japanese Patent Unexamined Publication No. Sho. 58-3672 discloses a coating method for forming a free falling curtain of a coating composition and coating a running web in which the opposite edge portions of the support are folded toward an uncoated surface side before the support is coated.
However, to coat webs of various different widths, it is necessary to make the width of a backup device (such as a backup roller, collars attached to the backup roller at its opposite end portions, etc.) coincident with the web to be coated. Accordingly, even if collars are attached to the backup roller for the purpose of width adjustment, the width cannot be changed continuously and smoothly, but must be changed in discrete steps. As a result, much time and labor are required to change the coating width.